In certain applications, it can be desirable to monitor the relative location or motion between two objects. For example, in certain applications, it can be beneficial to precisely direct a well-defined beam or sensing vector along particular directions or at specific locations with respect to a sample. It can therefore be important to provide knowledge about the relative location or motion between the beam or sensing vector and the sample. In several laser procedures, for example, it can be desirable to scan a laser beam across a sample according to a predetermined scan pattern or at specific locations. In cases where the sample may undergo uncontrolled motion, the precision with which the predetermined scan pattern or specific location can be achieved can be compromised. In certain sensing or imaging applications, it can be important to control the sensing point or axis with respect to a sample. In order to generate two- or three-dimensional images, the sensing point or axis can be scanned with respect to the sample according to a predetermined pattern. For accurate imaging reproduction of the structure of the sample, it can be important that the predetermined scan pattern is precisely followed. In the presence of uncontrolled sample motion, the actual scan pattern on or within the sample can differ from the predetermined scan pattern and image fidelity can be compromised.
One general category of strategies that can be commonly followed for monitoring the spatial location or motion between two objects is to monitor the location or motion of each objects with respect to a known or controlled reference point. This type of strategy can be relevant in cases where one object and the reference point are persistently located with respect to one another. In medical catheter-based imaging applications, for example, the signal transducer can be placed at the distal end of a catheter, which can be inserted within an animal or human body. The transducer can be connected to an actuator at a proximal end of the catheter using an axially non-extensible, torque-conveying element such that as the actuator rotates or pushes or pulls the element, the actuator's motion is replicated accurately at the transducer. When the tissue or organ that is being imaged is not moving, and further, when the imaging system is not moving, then the constraint that one object and the reference point can be fixed with respect to one another is met. Therefore, the relative location and/or motion of the transducer with respect to the organ or tissue can be monitored and controlled. In some cases, however, the organ or tissue may undergo motion, e.g., due to respiration, cardiac function, peristalsis or patient motion, and this general category of strategy may not be applicable. Further, motion within the body, along the length of the catheter, can result in an uncontrolled motion of a distal end and of the transducer of the catheter with respect to the tissue of interest.
In certain medical procedures, it can be preferable to monitor the location and/or motion of an instrument with respect to a specific anatomical location or organ. An exemplary strategy to accomplish this objective can be to prepare the instrument so that it can be detected by an imaging modality that also facilitates a detection of the specific anatomical location or organ. In certain cases, however, the anatomical location or organ may not exhibit sufficient contrast for detection. For example, by fluoroscopy or X-ray computed tomography, the soft-tissues of the body can exhibit low relative contrast. For example, coronary arteries may not, therefore, be located with these techniques without the use of exogenous contrast agents. Furthermore, certain conventional imaging technologies may not have a sufficient resolution to precisely determine the relative location or motion of an instrument with respect to a specific anatomical location or organ.
The above-described issues and deficiencies are merely representative of a need for more precisely monitoring the relative location or motion between two objects. Indeed, it may be beneficial to address and/or overcome at least some of the deficiencies described herein above.